import java.util.Scanner;

public class Java039 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double n=sc.nextDouble();

        double all=fun1(n);
        System.out.println(all);

    }
    public static double fun1(double n){
        if(n>2){
            return 1/n+fun1(n-2);
        }
        else {
            return 1/n;
        }
    }
}
